1. Field of the Invention
The present invention relates to concrete products and their methods of fabrication and, more particularly, to concrete manholes, lift stations, and like access chambers having coatings or linings on their surfaces for resisting attack by corrosive gasses.
2. Description of the Background Art
In the past, a plurality of products have been designed and utilized for controlling the movement of sewage fluids therethrough. Such sewage fluids are principally liquids that release corrosive gasses, for example hydrogen sulfide gas, which tend to deteriorate the product through which the fluids flow. The most common of such products are steel reinforced concrete manholes and lift stations. Manholes are those access chambers which initially receive the sewage fluids and then feed them to a lift station from which they are subsequently pumped. The lift station is an access chamber which acts to temporarily store and periodically move the fluids from manholes through force mains to a waste water treatment plant for processing. From the manholes, the fluid is fed by gravity, but at the lift station, submersible pumps compact and move the fluids to the waste water treatment plant. Manholes and lift stations provide access to an underground system of fluid handling.
Known access chambers are generally fabricated solely of concrete. Some are fabricated solely of fiberglass. Access chambers solely of fiberglass are very expensive and lack the necessary strength and weight required for larger applications. Access chambers solely of concrete lack corrosion resistance and, consequently, have short lives. They are, however, of sufficient strength and weight to maintain their position underground during operation and use.
For about the last fifty years it has been a common practice to provide the interior exposed surfaces of access stations with a separate elastomeric sheet to abate corrosion of the concrete by the corrosive gasses of the fluids. The most common material for such liners is polyvinyl chloride, PVC. Unfortunately, such liners are held in place by a T-lock configuration wherein coupling of the liner to the concrete is by spacer mechanical fingers only.
The T-lock configuration for PVC liners creates an inferior product which couples liner to concrete only along spaced lines of their interface. The "T's" are only imbedded a fraction of an inch in the concrete and can easily become dislodged. The present invention has no such deficiencies. In addition, the T-lock configuration requires increased work on-site to trim and heat weld the various component parts to form one integral member. The final product thus has excessive field work required to combine product components. This impairs product performance, performance thus becoming a function of the skill of the field personnel. The present invention is totally made in house with minimized field time, expense and errors.
The present invention comprises a concrete access chamber with corrosion inhibiting and abatement layers integrated with the concrete itself. Such layers include polyester gel coat and glass reinforced polyester resin which are integrally formed on the mold during the fabrication process. All interior layers are laid up on the mold prior to the concrete being poured. This increases accuracy of the various product components with respect to each other and for increased performance of the final product.
The prior art discloses several methods of prohibiting corrosive materials from contacting concrete products by providing the exposed surface with an elastomer to resist corrosion of the concrete. The first method of protecting concrete from corrosive materials employs a corrosive resistant liner that functions as a form for the placement of concrete during the fabrication of a concrete product. By way of example, U.S. Pat. Nos. 3,250,654, 3,532,132 and 3,380,259 to Rubenstein disclose cast-in-place composite reinforced structural material pipe-lines for laying in a trench or similar environment. Subsequent to the formation of the pipe-liner, the liner is placed within a trench to act as a forming means for pipe fabrication whereby a flowable mix of concrete, or similar material, is placed around, about, under and over the pipe liner. In all three patents to Rubenstein the pipe liners are formed by applying a layer of mold release to a mandrel. Then a plurality of forward moving strands or chopped strands are placed in position for spinning in a helical winding. The strands are subsequently wound at a selected helical angle. While the strands of glass fiber are being spun under tension onto the mandrel, a polymer resin composition having a catalyst is applied to the strands of fiber as they are layered upon the mandrel. As the composition reaches the desired state of cure, the pipe-liner is moved forward and removed from the mandrel. Finally, the pipe-liner is then placed within a trench or similar environment. Concrete or other porous material is placed around, about, over and under the pipe-liner to comprise a reinforced concrete pipe-line having corrosion resistant features. In all three disclosures the pipe-liner acts first as a forming means for casting a concrete cover component of the pipe-line and remains in place as a polymerized-polymeric-resin-composition-fiber-reinforced-pipe-liner. Additionally, the pipe-liner and concrete form a mechanical bond with finger-like projections from the exterior surface of the liner's bonding compound that project into the concrete material. The thickness of the concrete layer surrounding the liner and the placement of reinforcement cables within the concrete layer are provided by either rectangular or triangular shaped guides placed on the exterior surface of the pipe-liner.
Chandler et al U.S. Pat. No. 3,439,461; Singer U.S. Pat. No. 3,745,738 and Ditcher et al U.S. Pat. No. 4,751,799 disclose methods of providing plastic liners in concrete manholes. In Chandler et al a method of constructing burial vaults with a composite wall is disclosed. A plastic resinous liner is coated with a strong, wet, tacky adhesive bonding agent prior to concrete being placed on the liner to form a wall component. The concrete and bonding agent cure forming an integral bond between the liner and the concrete. The liner serves as a form or mold for forming the inner concrete wall component thereof. Alternately, Chandler et al discloses that the plastic resinous liner may be a coating that is applied to an existing concrete surface and allowed to cure to form a rigid liner.
In Singer, tubular sections of plastic including a base portion are secured to a conventional concrete slab in a ground hole. The tubular sections are stacked end on end vertically to form a manhole. A hollow shell is placed about the vertically aligned sections and laterally displaced therefrom. Concrete is then poured into the cavity formed by the outer wall of the tubular sections and shell. After the concrete has cured, the outer shell is removed. The plastic liner not only makes the concrete manhole corrosion resistant, but also acts as a form to mold the manhole to a desired configuration. Alternately, Singer discloses a method of spraying or blowing glass reinforced polyester plastic or other similar plastics onto existing structures to obtain corrosion resistance.
In Ditcher, the liners are comprised of a plurality of sections joined together to form the inner surfaces of the manhole and thus providing corrosive resistant surfaces to the concrete product. The liner section defines and forms the inner surface of the manhole being fabricated. Concrete, or similar material, is placed within the mold and allowed to set. The liner material acts to form and support the casting material during the curing process. Since the liner material does not bond naturally to concrete, the liner material engages the concrete by means of integral substantially T-shaped projections which anchor the liner sections to cast members.
A method of extruding and laminating prestressed reinforced concrete pipe is illustrated in Rubenstein U.S. Pat. No. 3,520,749. Polymerizable polymeric resin composition is applied over a mandrel that has been covered with mold release. A resin rich gel coat layer is formed to which glass fiber is applied under tension. The strands are then covered and impregnated with a polymerizable polymeric resin composition to form a pipe-liner. The pipe-liner is then covered with a bonding resin composition in a polymerizable state. Finally, the pipe-liner and mandrel are inserted into an extruder so that polymeric resin composition bonded concrete may be extruded around and about the pipe. The extruder exerts pressure on the concrete and liner to cause the components to bind together.
A second method of protecting concrete from corrosive materials employs a coating or liner material that is applied to an existing concrete product. By way of example, Sergovic U.S. Pat. No. 2,962,052 ; Rubenstein U.S. Pat. No. 3,177,902; Darrow U.S. Pat. No. 3,381,718 and Christensen U.S. Pat. No. 3,984,266 disclose protective materials that are applied to concrete products. In Sergovic, a coating is applied to a concrete pipe to increase wear resistance of the pipe. A polyester-sand coating is applied by means of a spray gun, brush or trowel. The coating may be applied to the exterior or interior of a pipe. The concrete pipe to be coated has a facing layer of a reaction product that is an ethylenically unsaturated alkyd resin and a polymerizable vinyl monomer and a filler. Minimal mechanical bonding takes place between the coating and substrate as a result of minimal surface openings in the concrete available for bonding.
In Rubenstein a method of enhancing the strength features of a porous material is disclosed. The surface, pores and interstices of the surface of porous material are filled and covered with a layer of tough, rubbery reinforcing polymerized resin composition having fiberglass strands under tension embedded with the resin. The resulting surface is more impact resistant to dynamic loading, but does not provide an enhanced surface with improved mechanical bonding between the coating and the substrate.
In Darrow a pipe having a lining material that is resistant to corrosion is disclosed. Two or more plies of a plastic liner are adhered to the inside surface of a concrete pipe. The liner material is backed by a material that is highly susceptible to secure bonding to concrete by a bonding agent. The liner and backing are bonded to the pipe by draping the lining material over an inflatable pneumatic tube assembly which is smaller than the inside diameter of the pipe. Adhesive is applied to the backing material or pipe or both, the tube with the liner draped thereupon are placed within the pipe. Finally, the tube is then inflated to effect contact between the lining and pipe. The disclosure relies on surface bonding between the backing material of the liner and concrete. Due to the limited adhesion available between the concrete surface and the backing material, a good mechanical bond is prohibited.
In Christensen a process for bonding glass reinforced plastic to a ferro-cement product is disclosed. After a ferro-cementious structure has cured, acid is applied to the surface to be protected for effecting etching of the surface. The surface is then rinsed, dried, and a coat of adhesive is applied to the surface. Glass fiber reinforced plastic is applied to the wet adhesive and allowed to cure. The coating results in a structure with improved impact resistance but without a strong mechanical bond between the coating and pipe. This results from minimal surface area available for mechanically bonding of the coating and concrete.
The third method of protecting concrete from corrosive materials is to form a solid structure that is cast with a smooth outer surface. By way of example, Bogue et al U.S. Pat. No. 3,654,018 discloses a structure that has a hard outer surface formed as a fiber-included resin lay-up of a hard material having an inner surface with hooked projections. The hooked projections are created by pulling material from the lay-up and allowing such to droop by gravity. A hardenable aggregate is deposited on the pre-fabricated inner surface which acts as a form for the structure. The aggregate interlocks with the inside surface to create the desired component shape.
None of the known commercial devices or prior patents disclose the present invention. Although many such prior advances are noteworthy to one extent or another, no prior patent or known device teaches or suggests the reliable, convenient and economical concrete products as disclosed herein. As illustrated by a great number of prior patents and devices, efforts are continuously being made in an attempt to more efficiently design, manufacture and utilize manholes, lift stations and the like in an attempt to more efficiently design, manufacture and utilize such product. No prior effort, however, suggests the present inventive combination of component elements arranged and configured as disclosed herein. Prior devices do not provide the benefits attendant with the present invention. The present invention achieves its intended purposes, objects and advantages over the prior art devices and methods through a new, useful and unobvious combination of method steps and component elements, through the use of a minimum number of functioning parts, at a reasonable cost to manufacture, and through the utilization of only readily available material and conventional components.
Therefore, it is an object of the present invention to provide a cost effective manhole/lift station type structure that utilizes a chemical and gas resistant fiberglass liner interwoven mechanically with the concrete and steel reinforcement of an outer structure that provides low cost ballast and strength and that also allows a system that utilizes existing conventional forms and procedures.
It is a further object of the present invention to abate the adverse effects of corrosive gasses on concrete products.
It is a further object of the present invention to extend the life of manholes, lift stations and like access chambers.
It is a further object of the present invention to provide access chambers with the strength of concrete and the corrosion resistance of fiberglass.
It is a further object of the present invention to manufacture superior manholes, lift stations and the like in an efficient, economical manner.
The foregoing has outlined some of the more pertinent objects of the invention. These objects should be construed to be merely illustrative of some of the more prominent features and applications of the intended invention. Many other beneficial results can be obtained by applying the disclosed invention in a different manner or modifying the invention within the scope of the disclosure. Accordingly, other objects and a fuller understanding of the invention may be had by referring to the summary of the invention and the detailed description of the preferred embodiments in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings.